Known photosensitive resin compositions for flexographic printing plate include compositions comprising a thermoplastic elastomer, a photopolymerizable unsaturated monomer, and a photopolymerization initiator, such as those described in JP-B-51-43374 and JP-B-59-22219 (the term "JP-B" as used herein means an "examined Japanese patent publication"). The photosensitive resin composition is exposed to active light rays through a mask having a prescribed pattern, and the unexposed area is washed away with a developing solution. Since the photosensitive layer comprises, for example, a hydrophilic thermoplastic elastomer, the photosensitive resin layer does not dissolve in water or an aqueous solvent so that chlorine organic solvents, such as chloroform, trichloroethane, trichloroethylene, and tetrachloroethylene, have been used as a developing solution.
Although the chlorine organic solvents are stable and easy to handle on account of their nonflammability, they not only involve health problems because of their high toxicity but also form one of the causes of destruction of the ozonosphere and are therefore unfavorable from the standpoint of working environment and environmental protection such as air pollution. For these reasons, it has been demanded to develop a non-chlorine developing solution. To this effect, a developing solution comprising an aromatic hydrocarbon and a paraffin or naphthene hydrocarbon at a specific volume ratio (see JP-A-5-134416, the term "JP-A" as used herein means an "unexamined published Japanese patent application") and an organic solvent system comprising a specific ester and an alcohol at a specific volume ratio (see JP-A-4-18564) have been proposed.
The developing solutions according to JP-A-3-322416 are less causative of health and environmental problems than the conventional chlorine organic solvents. However, besides giving off an unpleasant smell, they tend to swell the image area during the development, resulting in a failure of obtaining good image reproduction unless their composition is altered according to the thickness of the plate. Since the developing solution according to JP-A-4-18564 comprises a specific ester, it is expensive and cannot be supplied in large quantity at a low price.